Foreign Minister Bob Carr says a dinner at the G20 summit in Russia failed to reach consensus on how to respond to the use of chemical weapons in Syria.

Key points

Obama, Putin and Cameron among those attending the G20 summit

Bob Carr is representing Australia

Topic of whether to take military action against Syria dominates the summit

China says military action will have a negative impact on the economy

Uk claims to have new evidence that chemical weapons were used by Assad

Russian president Vladimir Putin invited world leaders to thrash out their differences over Syria at a dinner on the sidelines of the summit in St Petersburg, as United States president Barack Obama continues to push his case for military action in the face of strong Russian opposition.

Senator Carr, who is attending the summit on Australia's behalf, says leaders failed to reach a consensus on how to respond, but that he still expects the most likely course of action will be a military strike by the US.

"All countries expressed their views, there was no consensus and there was no hope of movement from the UN Security Council," he said.

"Hence we're back in the position, the pre-existing position, namely to enforce a global norm, [that] is an expectation from countries like Australia."

Russia has led opposition to US-led military action against Syrian president Bashar al-Assad over August 21's chemical attack outside Damascus, which Washington says was perpetrated by the Syrian regime.

In a new bid for a peaceful solution for Syria, the UN announced that its special envoy Lakhdar Brahimi was on his way to attend the summit to push for peace talks.

Russia meanwhile said Syria's foreign minister Walid Muallem would travel to Moscow on Monday as Mr Obama seeks to convince US lawmakers to approve military action.

No information filtered out about the exchanges at the closed-door dinner hosted by Mr Putin at the imperial palace of Peterhof outside Saint Petersburg.

Mr Putin and Mr Obama put on a show of smiles for the cameras as they shook hands just before the summit got under way on the shores of the Gulf of Finland.

Syria's allies remained unmoved by Mr Obama's push, with Iran's supreme leader Ayatollah Ali Khamenei calling allegations of a chemical weapons attack by the regime a "pretext" to launch strikes against the country, and pledging to support Damascus "until the end".

According to US intelligence, more than 1,400 people living in rebel-held suburbs of Damascus were killed in the strike, which involved the use of sarin nerve gas.

'War will not solve the problem'

Beyond convincing Russia, Mr Obama has a tough sell ahead elsewhere, with China - another veto-wielding Security Council member - having already expressed its "grave concerns" over unilateral military strikes.

Pope Francis added his voice to the calls for a peaceful solution to the Syria crisis, warning against "futile pursuit of a military solution".

German chancellor Angela Merkel has repeatedly ruled out her country's participation in any US-led military strike against Assad's regime, while the British parliament has also rejected the idea.

EU president Herman van Rompuy said while the Damascus chemical attack was "a crime against humanity" there is "no military solution to the Syrian conflict".

Mr Brahimi was in St Petersburg to help secretary general Ban Ki-moon push at the G20 summit for an international peace conference on Syria, first proposed by the US and Russia in May.

"Providing more arms to either side is not the answer. There is no military solution," the UN quoted Ban as telling the G20 leaders.

Obama unlikely to be deterred by those against military strikes

Mr Obama is unlikely to be deterred.

He said before talks with Japan's prime minister on the sidelines of the summit, that the use of chemical arms in Syria was "not only a tragedy but also a violation of international law that must be addressed".

Aides said he would set out his views at the leaders' dinner and hoped to build support for military action against president Bashar al-Assad's regime, although aides acknowledge a consensus might be hard to find.

We would not anticipate every member of the G20 agreeing about the way forward in Syria, particularly given the Russian position over many, many months now in terms of resisting efforts to hold the Assad regime accountable.

White House deputy national security adviser Ben Rhodes

"We would not anticipate every member of the G20 agreeing about the way forward in Syria, particularly given the Russian position over many, many months now in terms of resisting efforts to hold the Assad regime accountable," White House deputy national security adviser Ben Rhodes said.

Mr Putin was isolated on Syria at a Group of Eight meeting in June, the last big summit of world powers, but could now turn the tables on Mr Obama, who recently likened him to a "bored kid in the back of the classroom" who slouches at meetings.

Only France, which has already said it is preparing to join US military action, rallied loudly behind Mr Obama.

"We are convinced that if there is no punishment for Mr Assad, there will be no negotiation," French foreign minister Laurent Fabius said before leaving for St Petersburg.

With backing by Beijing and Moscow unlikely at the Security Council, where both have veto powers, Mr Obama is seeking the approval of the US Congress instead.

Mr Putin says rebel forces may have carried out the poison gas attack and that any military strike without Security Council approval would violate international law, a view now being supported increasingly openly by others - including countries that have usually disagreed with Moscow on Syria.

The Russian president's press secretary, Dmitry Peskov, portrayed the "camp of supporters of a strike on Syria" as divided, and said: "It is impossible to say that very many states support the idea of a military operation."

Mr Peskov also reiterated that the United States had failed to produce convincing proof that Mr Assad, who is backed by Russian arms, and his forces had resorted to chemical warfare.

German chancellor Angela Merkel saw no chance of agreement between Mr Putin and Mr Obama on Syria.

US-Russian ties have long been strained by political differences but went into freefall when Russia harboured Edward Snowden, a former spy agency contractor who leaked details of US intelligence programs.

Any G20 decision on Syria would not be binding, but Mr Putin would like to see a consensus to avert military action in what would be a significant - but unlikely - personal triumph.

But with Russia expected to use its UN Security Council veto to block any military action, US ambassador to the UN Samantha Power accused Russia of holding the Security Council "hostage" over the Syria crisis.

UK has new evidence of Syrian chemical weapons use

Meanwhile, Britain has new evidence that chemical weapons were used in an attack on Damascus, Mr Cameron said.

Mr Cameron said scientists at Britain's Porton Down military research facility had analysed samples taken from the August 21 attack and concluded they had tested positive for the sarin nerve gas agent.

"We have just been looking at some samples taken from Damascus in the Porton Down laboratory in Britain which further shows the use of chemical weapons in that Damascus suburb," he said.

Mr Cameron lost a parliamentary vote last week backing military action to punish Syria for the attack.

But the British leader denied this had left him on the sidelines of talks at the G20.

"Not in the slightest," he said when asked if he had no hand to play at the summit, adding Britain would be "leading the argument on humanitarian aid".

Mr Cameron also said Mr Obama was right to press ahead with possible military strikes against Syria as Mr Assad had ignored his warnings about using chemical weapons during the country's teo-and-a-half-year civil war.

"I absolutely believe that, having set a red line on the further big use of chemical weapons, it would be wrong if America was to step back and, having set that red line, to do nothing," he said.

"I think that would send an appalling signal to president Assad and also to dictators elsewhere."